Interstate 435and Front Street

Interchange Improvements

Project Location

Purpose and Need for this project

To provide safety improvements at the northbound and southbound exits from I-435, within the interchange on Front Street and the entrance ramp onto southbound I-435.

Project Scope

Initial Concepts We Reviewed

Single Point (SPUI)

Half-Cloverleaf

Roundabout

Tight Urban Diamond (TUDI)

Single Point (SPUI)

Problems with a Single Point design

Required extensive reconstruction of I-435.

Costs for additional right-of-way and construction were very high, about$31 million.*

We had concerns about how long it would take trucks to clear such a large intersection.

*Based on 2002 estimates.

Half-Cloverleaf

Problems with a Half- Cloverleaf design

Required large amounts of new R/W.

Costs for additional right-of-way and construction were very high, about$37 million.*

We had concerns about the trucks being able to accelerate from the loop ramps onto the freeway.

*Based on 2002 estimates.

Roundabout

Problems with a Roundabout design

Did not perform as well as other alternatives.

We had concerns about the operation of the trucks in the roundabout (two trucks likely would not enter a roundabout at the same time, reducing capacity).

Costs for additional right-of-way and construction, about $10 million.*

*Based on 2002 estimates.

Tight Urban Diamond (TUDI)

Problems with a Tight Urban Diamond design

Required considerable reconstruction of I-435.

Did not work as well as the SPUI or half-cloverleaf.

Costs for additional right-of-way and construction were high, about$28 million.*

*Based on 2002 estimates.

Initial Design

Initial Design

The existing interchange is very similar to a TUDI, with I-435 over Front Street.

The initial preliminary design included:Adding lanes to the off ramps with

double and triple left turn lanes.Adding lanes to Front Street

between Universal and Corrington with traffic lanes behind the bridge piers.

Problems with the initial design

The life of the capacity improvements were limited. This design would probably fail within 10 to 15 years.

The Levels of Service were D, E and F.Costs for additional right-of-way and

construction were still somewhat high, about $11 to $12 million.*

This design has 45 conflict points within the entire interchange.

*Based on 2005 estimates.

Conflict Point Diagram - TUDI

Problems with the initial designTriple left turn lanes were needed for the

northbound to westbound movement. This is not desirable with 11% trucks during peak hour. (Off peak has about 30% trucks.)

Seven lanes were needed under the bridges, requiring construction of lanes and retaining walls behind the bridge piers in existing sand fills. This would be difficult to build.

The trucks required large turning radii to achieve capacity improvement. This limited vehicle storage between the signals.

A Practical Design Solution

A Diverging Diamond Interchange or DDI

Diverging Diamond Design

Link to DDI overhead videoLink to one of the drive thru videos

Advantages of using a DDI at this Location

The DDI doubles the capacity of the left turn lanes and eliminates the need for the triple left turn. The double left turn should be safer than a triple with high truck volumes.

Levels of Service are A, B and C.This design reduces the number of

lanes required under the bridge to four, eliminating the need to build retaining walls.

AdvantagesThis also reduces the number of lanes

needed on Front Street beyond the interchange.

This DDI design has more storage room between the ramp signals.

(550’ vs 350’)

This design will also provide better sight distance. Drivers on the ramps don’t have to look through bridge columns to see on-coming traffic.

AdvantagesIt incorporates roadway features which

calm traffic and reduce speeds while maintaining capacity. This should result in fewer and less severe crashes.

Although wrong way entry into opposing lanes is possible, wrong way entry onto the ramps and the interstate will be almost eliminated.

The DDI has 21 conflict points compared to 45 with the initial design.

Conflict Point Diagram - DDI

AdvantagesThe smaller ramp intersections

mean vehicles will have shorter clearance times resulting in less exposure and safer conditions.

The DDI design has reduced the cost of the project.

Estimated Costs* Initial DDI Construction

MoDOT $ 6,763,000 $4,097,000Kansas City $ 103,000 $ 71,000

Right of WayMoDOT $ 1,823,000 $ 625,000Kansas City $ 2,045,000 $ 667,000

Utility Relocations MoDOT $ 600,000 $ 312,000

Total Costs $11,334,000 $5,772,000*Based on 2005 estimates.

Disadvantages of a DDIDriver expectations.We need more extensive public

involvement.Pedestrians have to cross free-flowing

ramps (or the crossings need to be signalized as at this location).

There is very limited accident history available.

We need additional signing, lighting and pavement markings.

DDI One construction season

Length of Construction

Two construction seasons

TUDI

ConclusionThe DDI will improve safety and

capacity of the existing interchange, at less cost and with a shorter construction schedule.

It will also provide valuable information on function and safety that will allow MoDOT and FHWA to determine if use of the DDI design at other locations is feasible.